It has been proposed in the past to use Josephson devices in an analog to digital (A/D) converter. Due to their high speeds, the Josephson devices have great potential for use in an A/D converter. However, to date, the performance achieved by previous superconducting converters has been relatively poor, due to the limited state of the art in fabrication and the circuit topologies used.
In one known design of an n-bit A/D converter using Josephson devices, each of the interferometers divides a sampled input analog signal differently, in order to weight the bits output by each interferometer. This is known as weighting by periodicity. The concatenation of the weighted bits is a digital representation of the analog signal. Thus, the signal to the interferometer which produces the most significant bit will be divided by two, for example, while the signal to the interferometer producing the least significant bit is divided by a larger number, 32 for example. In general, in an n-bit A/D converter, the signal to the interferometer producing the least significant bit needs to be divided into 2.sup.n-1 identical periods. Interferometers capable of a relatively large number of identical periods will have high internal inductance, with slow speed and threshold shifts due to input slew rate. There is therefore a problem in using interferometers which are weighted by periodicity in an A/D converter.